[meteorite-list] Pace Quickens for NASA Spacecraft Orbiting Mars (MRO)

[Ron Baalke]

Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.                                      

Erica Hupp 202-358-1237
NASA Headquarters, Washington, D.C.

News Release: 2006-085                                      June 19, 2006

Pace Quickens for NASA Spacecraft Orbiting Mars

NASA's newest spacecraft at Mars has already cut the size and duration of each 
orbit by more than half, just 11 weeks into a 23-week process of shrinking its 
orbit. By other indicators, the lion's share of the job lies ahead.

"The orbits are getting shorter and shorter. We've finished about 80 of them so far, 
but we have about 400 more to go, and the pace really quickens toward the end," 
said Dan Johnston, Mars Reconnaissance Orbiter deputy mission manager at NASA's 
Jet Propulsion Laboratory, Pasadena, Calif.

Supplementing the daily attentions of navigators, engineers and scientists, the 
orbiter has begun using unprecedented onboard smarts to schedule some of its own 
attitude maneuvers during each orbit.

The current phase of the Mars Reconnaissance Orbiter mission, called "aerobraking," 
began in late March with the spacecraft in a pattern of very elongated, 35-hour 
orbits.  It will end in early September, according to current plans, once hundreds 
of careful dips into Mars' atmosphere have adjusted the orbit to nearly circular, 
two-hour loops. Then, after some touch-up engine burns, deployment of a radar 
antenna and other transitional tasks, the spacecraft will be in the right orbit 
and configuration to start its main science phase in November.

During the two-year science phase, Mars Reconnaissance Orbiter will examine Mars 
from subsurface layers to the top of the atmosphere. It will use its 3-meter 
(10-foot) diameter dish antenna to pump data Earthward at up to 10 times the pace 
of any previous Mars mission. Besides providing information about the history and 
extent of Mars' water, the orbiter will assess prospective landing sites for NASA 
robots launching in 2007 and 2009.

When the spacecraft first entered orbit around Mars, its farthest point from the 
planet was about 45,000 kilometers (28,000 miles). After 11 weeks of aerobraking 
operations, this distance has been reduced to about 20,000 kilometers (12,000 miles). On each orbit since early April, the nearest-to-Mars portion of the orbit has 
passed through the upper atmosphere, usually at about 105 kilometers (65 miles) 
above the surface of the planet. The drag created by interaction of the atmosphere 
with spacecraft surfaces slows the craft.

"Our biggest challenge is the variability of the atmosphere," Johnston said. "It's 
not uncommon to get a 35 percent change in how much drag the spacecraft experiences 
from one pass to the next. We need to monitor each pass carefully and be prepared 
to change the altitude to a safe one for the next pass, if necessary."

While the orbiter is above the atmosphere, it can orient its antenna toward Earth 
and its solar panels toward the sun.  Before it enters the atmosphere for each pass, 
it pivots so that the back surfaces of the solar panels and antenna face the 
direction of travel.  An innovative capability of Mars Reconnaissance Orbiter's 
onboard software enables it to calculate the time when it needs to reorient itself 
for the next pass. This feature, called "periapsis timing estimator," was activated 
in May.

JPL's Jim Graf, project manager for Mars Reconnaissance Orbiter, said, "In the past, 
the times for turning to aerobraking attitude had to be calculated on the ground 
and sent to the spacecraft for each pass.  Now, the spacecraft can do that itself. 
This will be especially helpful when the spacecraft gets to the point when it is 
doing several drag passes per day."

Mars Reconnaissance Orbiter is the third NASA Mars mission -- after Mars Global 
Surveyor in 1997 and Mars Odyssey in 2001 -- to use aerobraking to get into a 
desired, near-circular orbit.  The strategy allows launching the spacecraft with 
much less fuel than would be required if using just rocket engines to decelerate 
into the desired orbit. Each drag pass this month is slowing Mars Reconnaissance 
Orbiter by an average of about 2 meters per second (4.5 miles per hour), which 
would otherwise require consuming about a kilogram (2.2 pounds) of fuel.

Transition activities during the two months between the end of aerobraking and the 
beginning of the main science phase will include unfolding two 5-meter (16-foot) 
lengths of antenna for a ground-penetrating radar instrument, removing the lens cap 
from a mineral-identifying spectrometer instrument and characterizing all 
instruments' performance in different modes of use. From early October to early 
November, Mars will be nearly behind the sun as viewed from Earth.  Communication 
with all spacecraft at Mars will be unreliable during portions of that period, so 
commanding will be minimized.

Additional information about Mars Reconnaissance Orbiter is available online at 

http://www.nasa.gov/mro .

The mission is managed by JPL, a division of the California Institute of 
Technology, Pasadena, for the NASA Science Mission Directorate, Washington. 
Lockheed Martin Space Systems, Denver, is the prime contractor for the project 
and built the spacecraft.

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